I've seen this on the internet before.
I have a Ubuntu server with a 4 port gigabit network card.
I would like to bridge the interfaces so that, if an interface is busy, the packets will go through an interface that isn't being used.
The term is NIC Bonding, or NIC Teaming.
Nic bonding is defined as bonding of two or more network cards on a server/pc to form a parallel single connection. This is a great way of achieving redundancy to a server if it's having more number of network cards.
Tutorials on the Internet abounds on how to do this. Explaining this can take several pages to show all options.
Some of note are:
Here is an example of an active-backup set up from the Ubuntu documentation:
# eth0 is manually configured, and slave to the "bond0" bonded NIC auto eth0 iface eth0 inet manual bond-master bond0 bond-primary eth0 # eth1 ditto, thus creating a 2-link bond. auto eth1 iface eth1 inet manual bond-master bond0 # bond0 is the bonding NIC and can be used like any other normal NIC. # bond0 is configured using static network information. auto bond0 iface bond0 inet static address 192.168.1.10 gateway 192.168.1.1 netmask 255.255.255.0 bond-mode active-backup bond-miimon 100 bond-slaves none
(Note: this is just an example, one should read at least the Ubuntu documentation on this before doing this!)
To quote Wikipedia:
A network bridge is a computer networking device that creates a single aggregate network from multiple communication networks or network segments. This function is called network bridging. Bridging is distinct from routing. Routing allows multiple networks to communicate independently and yet remain separate, whereas bridging connects two separate networks as if they were a single network. In the OSI model, bridging is performed in the data link layer (layer 2). If one or more segments of the bridged network are wireless, the device is known as a wireless bridge.
An example of bridging would be connecting a computer to a WAN (internet) and LAN (work) network and the computer being able to go to both networks. It could also include making other computers on the LAN being able to go to the Internet via the PC that is connected to both.